Re: A Problem with Page Cache in Xen

[Tim Deegan <tim@xen.org>]

Hello, 

Please don't top-post. 

At 15:01 +0800 on 31 Jan (1328022097), hxkhust wrote:
> Is the (prototype) memory-sharing code mentioned in your last email
> already offered in Xen resource code?

Yes; see changeset 20693:617071a8c638 and thereabouts.  But that code
went in about two years ago, and has been unmaintained since then, so I
would be very surprised if it's working now.  

You should also look at the recent patches that Andres Lagar-Cavilla has
been sending, whioch update the hypervisor side of the page-sharing
code. 

Cheers,

Tim.

> At 2012-01-30 17:47:31,"Tim Deegan" <tim@xen.org> wrote:
> >Hi,
> >
> >At 16:11 +0800 on 30 Jan (1327939919), hxkhust wrote:
> >> On a physical machine with xen virtualization platform installed ,VM
> >> A,VM B are VM C's virtual disks are all image files,among which VM A
> >> and VM B's virtual disks are QCOW2 format and VM C's disk is RAW
> >> format. And VM A and VM B's virtual disk image files are based on VM
> >> C's virtual disk image file.Now these three VMs are running on the
> >> same physical machine with xen installed. In the process of running VM
> >> A get a page data from VM C's virtual disk image file. After that ,VM
> >> B also need to get the same page data as VM A got just now.Under this
> >> situation, does VMM copy the page data from VM A's memory to VM B's
> >> memory or get the page data from VM C's virtual disk image file in the
> >> physical disk again?
> >
> >It reads it from the disk again, unless you're using the (prototype)
> >memory-sharing code that's in blktap.
> >
> >> Or if I would like to figure out this problem,what shall I do?
> >
> >Instrument the disk, or read the code.